The more than 60 ternary carbides and nitrides, with the general formula Mn+1AXn—where n = 1, 2, or 3; M is an early transition metal; A is an A-group element (a subset of groups 13–16); and X is C and/or N—represent a new class of layered solids, where Mn+1Xn layers are interleaved with pure A-group element layers. The growing interest in the Mn+1AXn phases lies in their unusual, and sometimes unique, set of properties that can be traced back to their layered nature and the fact that basal dislocations multiply and are mobile at room temperature. Because of their chemical and structural similarities, the MAX phases and their corresponding MX phases share many physical and chemical properties. In this paper we review our current understanding of the elastic and mechanical properties of bulk MAX phases where they differ significantly from their MX counterparts. Elastically the MAX phases are in general quite stiff and elastically isotropic. The MAX phases are relatively soft (2–8 GPa), are most readily machinable, and are damage tolerant. Some of them are also lightweight and resistant to thermal shock, oxidation, fatigue, and creep. In addition, they behave as nonlinear elastic solids, dissipating 25% of the mechanical energy during compressive cycling loading of up to 1 GPa at room temperature. At higher temperatures, they undergo a brittle-to-plastic transition, and their mechanical behavior is a strong function of deformation rate.

MXenes are prone to oxidize and degrade quickly in a matter of days. Here, the use of antioxidants, such as sodium L-ascorbate, is demonstrated as an effective approach to arrest the oxidation of colloidal and dehydrated Ti 3 C 2 T x MXene nanosheets. The success of the method is evident as the Ti 3 C 2 T x nanosheets maintain their composition, morphology, electrical conductivity, and colloidal stability. This method addresses the most pressing challenge in the field of MXene engineering.

Ti 3 C 2 T x belongs to the family of MXenes, 2D materials with an attractive combination of functional properties suitable for applications such as batteries, supercapacitors, and strain sensors. However, the fabrication of devices and functional coatings based on Ti 3 C 2 T x remains challenging as they are prone to chemical degradation by their oxidation to TiO 2. In this paper, we examine the oxidation of Ti 3 C 2 T x in air, liquid, and solid media via conductivity measurements to assess the shelf life of Ti 3 C 2 T x MXenes. The oxidation of Ti 3 C 2 T x was observed in all the media used in this study, but it is fastest in liquid media and slowest in solid media (including polymer matrices). We also show that the conventional indicators of MXene oxidation, such as changes in color and colloidal stability, are not always reliable. Finally, we demonstrate the acceleration of oxidation under exposure to UV light.

In this study, we successfully demonstrate the electrochemical etching of Al from porous Ti2AlC electrodes in dilute hydrochloric acid to form a layer of Ti2CTx MXene on Ti2AlC.